A sodium chloride spring with sulfate adding quiet body, drawn from a source that reaches 94.6 °C, among Japan's hottest natural sources. Mildly alkaline and soft on the skin, it is moderately mineralized with noticeable body, and a generous 106.6 mg/kg of metasilicic acid leaves a thin silica film that places it in the beauty-water family; for bathing it is documented for dry skin and cuts. It is also one of the rarer sources approved for drinking, documented for constipation and atrophic gastritis, though the posted notice caps intake at 220 ml a day because the water contains arsenic.
Good for
Warming
Salt forms a film on the skin that slows heat loss, so the warmth lingers long after the bath (the classic heat-keeping water, netto 熱の湯).
cold sensitivity
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
Aches & joints
Warmth eases stiffness and raises the pain threshold. Radon and sulfate springs show the strongest evidence for joint and muscle pain.
stiff shoulders
Smooth skin
Bicarbonate and alkalinity gently lift dead keratin while silica hydrates, leaving skin smooth. This is the basis of the beautifying-water (bijin-no-yu 美人の湯) reputation.
dry, rough skin
Gut & metabolic
Bicarbonate and sulfate waters, taken as a drink, neutralize stomach acid and help with constipation and gout.
stomach, gout (drinking)
Cuts
Mineral-rich chloride, sulfate and sulfur waters have a long-recorded soothing effect on minor cuts and slow-healing skin.
minor wounds
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Take care
From a certificate analyzed in 2018.
- Active stage of any illness (especially with fever)
- Active tuberculosis
- Marked physical debility, such as advanced malignant tumor or severe anemia
- Severe heart or lung disease causing breathlessness on slight exertion
- Severe kidney disease with edema
- Gastrointestinal bleeding
- Visible bleeding
- Acute exacerbation of a chronic illness
- Hyperthyroidism, when drinking more than 160 ml of the water a day
Full composition
The bar is each ion's share of charge (mval%) within its group; over 20% names the spring. Gases, silica and trace metals are measured by mass only.
- Sodiumsalt's cation: pairs with chloride to make the water saltyNa⁺391mgP71 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺48.8mgP57 national
- Potassiumminor; matters for drinking limitsK⁺11.1mgP47 national
- LithiumLi⁺0.60mgP59 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.05mgP30 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.03mgP14 national
- Magnesiummild; a laxative if you drink itMg²⁺0.02mgP4 national
- Manganesetrace; companion to iron springsMn²⁺< —mg
- ZincZn²⁺< —mg
- Chloridetable-salt anion: coats the skin and holds heat inCl⁻432mgP74 national
- Sulfate"gypsum / Glauber's salt": vessels and wound healingSO₄²⁻332mgP76 national
- Bicarbonate"soda": softens skin, leaves it smoothHCO₃⁻47.2mgP29 national
- Fluoridetrace; drinking limits applyF⁻5.7mgP80 national
- Bromidetrace, sea-originBr⁻1.1mgP62 national
- Hydrogen sulfidesulfur character: antibacterialHS⁻1.0mgP68 national
- Iodideyellows in air; helps blood lipidsI⁻0.60mgP74 national
- Thiosulfateoxidized sulfurS₂O₃²⁻0.60mgP64 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻0.40mgP14 national
- Metasilicic acidmetasilicic acid: a natural moisturizer for silky skinH₂SiO₃107mgP56 national
- Metaboric acidmetaboric acid: mildly antibacterialHBO₂27.2mgP79 national
- Metaarsenious acidHAsO₂0.60mgP82 national
- Free carbon dioxidefizz: widens blood vessels (strong above 1000 mg/kg)CO₂0.80mgP15 national
- Free hydrogen sulfide"egg" smell: opens vessels, antibacterialH₂S0.10mgP58 national
- Mercurytoxic trace: part of the drinking-safety checkHg0.0007mgP58 national
- CadmiumCd< —mg
- CopperCu< —mg
- LeadPb< —mg
Measured at the source
On the certificate
From a certificate analyzed in 2018.
- Chronic muscle or joint pain or stiffness (the chronic phase of rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains and the like)
- Reduced gastrointestinal function (heaviness, bloating)
- Impaired glucose tolerance (diabetes)
- Mild asthma or emphysema
- Stress-related symptoms (sleep disorders, depressed mood)
- Atrophic gastritis
- Constipation
- Biliary tract dysfunction
Evidence
- Maeda M. 温泉の医学的効果とその科学的根拠. J. Hot Spring Science 70:197–207, 2021.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- Tei C, Kihara T. Waon Therapy for Chronic Heart Failure. J. Cardiology 53(2):214–218, 2009.
- Coavoy-Sánchez SA et al. Hydrogen sulfide and dermatological diseases. Int. J. Dermatology, 2019.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Toriyama T et al. Carbon dioxide foot bathing on critical limb ischemia. International Angiology 21(4):367–373, 2002.
- Donaubauer AJ et al. Serial radon spa therapy on pain in musculoskeletal disorders. Frontiers in Immunology, 2024.
- Verhagen AP et al. Balneotherapy for rheumatoid arthritis. Cochrane Database of Systematic Reviews CD000518, 2015.
- Li H et al. Bicarbonate Ionized Water Bathing Enhances Natural Killer Cell Activity. Scientific Reports 14:51851, 2024.
- Matsumoto S et al. Hot spring bathing and HbA1c in type 2 diabetes. J. JAPMC 73(3):163–170, 2010.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.